The need to prolong shelf-life of food products, in particularly fresh produce, without harming quality, is well recognized. Many coating formulations are disclosed in the literature.
One of the known methods for coating fresh produce such as onions and edible fungi is to form a coating by applying to the exterior surfaces of onions or fungi a gelation solution comprising a hydrocolloid such as sodium alginate, and cross linking the hydrocolloid on the surface by a solution comprising a gelation inducing agent, such as CaCl.sub.2.
The so-obtained coating is both biodegradable and edible, and provides a protective coating to the treated vegetable. U.S. Pat. No. 3,865,962 discloses a process for coating raw onion products by immersion of the onion in an aqueous dispersion containing water soluble algin and subsequently treating the coated onion with an aqueous calcium ion to induce gelation.
EP 277 448 discloses an edible coating containing gelatin and polysaccharide. A cross-linking agent containing calcium ions is used for obtaining the coating.
U.S. Pat. Nos. 5,198,254 and 5,376,391 are directed to increasing the stability of fruits, vegetables and fungi by coating same with a composition comprising a polysaccharide polymer, a preservative an acidulant and two emulsifiers including lecithin, as well as optionally at least one antioxidant, a plant growth regulator and/or a chilling injury protectant. The polysaccharide polymer is preferably carboxymethylcellulose, but instead may be another hydrocolloid. Regardless, the polysaccharide polymer, even if a hydrocolloid, is not of the type which can undergo gelation without a gelation inducing agent, and these patents only involve drying of the coating composition on the product to be protected, and never gelation.
Moreover, none of the prior art documents discloses a coating containing in its matrix a compound having a specific reference to the surface of the product to be coated.